1. Field of the Invention
The present invention relates to a wafer level package for a SAW (surface acoustic wave) device and a fabrication method thereof.
2. Description of the Related Art
A surface acoustic wave (hereinafter, referred to as SAW) device is used as an electronic part for filters, delay lines and oscillators in an electronic device which transmits and receives a signal waveforms , and is widely used in the radio-frequency area for cellular phones, in order to filter unnecessary signals. There is a premium on compactness and enhanced-performance devices, as well as downward pressure on manufacturing cost.
A structure of a filtering device [SAW filter 10] manufactured by use of the SAW device in the prior art will be described through FIG. 1A and 1B. As described, the SAW filter 10 includes a ceramics package 11, a cavity part 12 formed by the walls inside of the package 11, a metal cap 13 sealing an opening of the cavity part 12 and a SAW element 14 embedded in the cavity part 12. As illustrated in FIG 1B, the package 11 is 3-layered structure where 3 substrates 11a, 11b, and 11c are joined, and formed with an electrode pad 15, a wiring pattern 16 and a foot pattern 17, respectively. The SAW element 14 is fixed on a bottom of the cavity part 12, with the surface with an InterDigital Transducer (hereinafter, referred to as IDT) on it put faceup. The SAW element 14 is electrically connected to the wiring pattern 15 exposed internally into the cavity part 12 by the metal wire 18. The metal cap 13 is fixed on an upper surface of the package 11 by a binding material 19 such as a solder or a resin.
The above structured SAW filter 10 is limited in being compact-sized, because the SAW filter 10 electrically connects the SAW element 14 to the package 11 by use of a wire in order to seal the embedded SAW element 14, and the metal cap 13 is joined on the upper side of the package 11. Also, the smaller SAW element 14 is, the more complicated it is to manufacture the SAW filter 10, and accordingly manufacturing costs increase.
Various methods using wafer level packaging technology have been under development to achieve a compact-sized SAW device. In particular, a method of implementing an integrally combined device by joining the SAW device and a wafer made of Silicon (Si) has been attempted. However, there are many problems due to the different thermal expansions of the different materials used in the SAW device and the wafer.